So, I read an article which was explaining why it makes sense to cohabitate before marriage. And I now have more insight into two things, namely why people feel that you'd get to know someone better when you were living together and not married (remember, if you live together for 8 years or so, the divorce risk is now down to normal, it's no longer elevated), and why the divorce risk might be higher.
The woman explained to her boyfriend that she was going to need extra closet space, and was horrified and surprised when he explained that he was going to want half of it. This comes as a surprise? I'm not going to try to justify what he did (but honestly, she shouldn't be expecting extra closet space), but how could she move in with him without knowing this? The other big surprise, was apparently that he didn't want to share laundry with her.
If you use moving in together to replace actually talking to each other, and think that moving in with someone is a better way to get to know them than just actually getting to know them is, then of course you're going to think that moving in together is necessary, because you can't know if you'll get along with them before you live together. (Oh, and by the way - I know that trying to live in the same house, but with two different households works for some couples, but it's not a great sign). And if you observe instead of talking, and have set ideas of what each person deserves (no negotiation over closet space or laundry?) I really can't see things working well if the going gets tough. Now I'm curious about how much damage the "never get married before 25" would cause along some of these same lines.